1. Field of the Invention
The present invention relates to a method of positioning objects to be measured and more particularly, it relates to a method preferably used for positioning semiconductor wafers through the probe apparatus.
2. Description of the Related Art
Probe measurement is one of those measurements employed in the course of manufacturing semiconductor devices such as transistors and integrated circuits. The probe measurement comprises electrically connecting matrix like semiconductor chips formed by pattern-form technique on a semiconductor wafer to a measuring circuit, which consists of measuring devices and others, through probes of the prober to measure electric properties of the semiconductor chips.
More specifically, the wafer measurement through the prober comprises placing the wafer on a table movable in directions X, Y and Z which are crossed one another at right angles and also rotatable in direction .theta. on a plane which includes directions X and Y, arranging a probe card provided with probes above and opposite to the wafer and successively contacting the probes of the probe card with each semiconductor chip on the wafer while index-moving the table.
However, the positional accuracy of attaching the probe card is low and this makes it difficult to accurately contact the probes with electrode pads of the semiconductor chips. When the wafer measurement is to be conducted, therefore, it is needed that a lot of the electrode pads on the surface of the semiconductor chips are previously positioned relative to a lot of the probes.
This positioning of the electrode pads relative to the probes was conventionally carried out by rotating the probe card to correct it in direction .theta. and moving the table in directions X and Y.
When the probe card must be rotated, however, a system for rotating the probe card is additionally needed to make the apparatus large in size. Further, its measuring line is made complicated and this makes it impossible to obtain accurate measuring results. Therefore, a technique of correcting the wafer in direction .theta. without using the rotating system for the probe card but while rotating the table has attracted attention these days. This technique is disclosed in Japanese Patent Application Publication (KOKAI) No. 60-59746, for example.
The technique disclosed by No. 60-59746 comprises placing a wafer on the table, directing the probes of a probe card in directions X and Y (which denote a coordinate system of the probes), rotating the wafer with reference to this probes-arranged direction to make the electrodes-arranged direction (which denotes a coordinate system of the electrodes) of semiconductor chips on the wafer parallel to the coordinate system of the probes, and moving the semiconductor chips on the coordinate system of the probes to position the electrodes of the semiconductor chips relative to the probes of the probe card.
When wafers belong to a same kind and they are always placed on the table at a same position, therefore, it may be arranged that the angle of the table rotated and the distance of the table moved in directions X and y are calculated relating to the first sheet of wafer and that they are stored. When arranged like this, electrode pads of the semiconductor chips on the second sheet of wafer and the following ones can be automatically positioned relative to the probes of the probe card by rotating the table at the angle stored and moving it in directions X and Y only by the distance stored.
However, the position of every wafer mounted on the table becomes different from one another. In addition, the center position round which each of the wafers is rotated is shifted from one another. The distance that the table is moved to position the wafer relative to the probe card is thus made different for every wafer. This makes it impossible to achieve the above-described automatic positioning and makes it necessary to carry out the positioning relative to every wafer. The throughput of this probe measurement is thus left low.
In the case of the above-described positioning method, it is needed that the electrode coordinate system of the semiconductor chips is aligned with the probe coordinate system of the probe card and that the chips on the whole area of the wafer are then successively probed. The accuracy of probing the chips on the wafer must be quite high, ranging to several microns. It is therefore quite insufficient that the probing direction is aligned only with the direction of the probe card. Even when the position of the probe card is aligned with one of the semiconductor chips on the wafer, it is sometimes finely shifted from those positions of the other chips on this wafer. It is therefore conventionally needed that chips on the whole areas of every wafer are searched, that the wafer is corrected in direction .theta. by hand and that the probing is started after the positioning of the wafer relative to the probe card. This makes the operation throughput reduced to a great extent.